Information Notice 1987-19, Perforation and Cracking of Rod Cluster Control Assemblies
SSINS No.: 6835 IN 87-19
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C.
20555
April 9, 1987
IE INFORMATION NOTICE NO. 87-19:
PERFORATION AND CRACKING OF ROD
CLUSTER CONTROL ASSEMBLIES
Addressees
All Westinghouse nuclear power pressurized-water reactor (PWR) facilities
holding an operating license or a construction permit.
Purpose
This notice is provided to inform recipients of a potentially significant
safety problem that could result from the perforation and cracking of the rod
cluster control assemblies (RCCAs) in Westinghouse PWRs.
It is expected that
recipients will review the information for applicability and consider action, as appropriate, to preclude a similar problem from occurring at their facili- ties.
However, suggestions contained in this information notice do not consti- tute NRC requirements; therefore, no specific action or written response is
required.
Description of Circumstances
An estimate that was intended to be conservative indicated that the RCCAs would
last for at least 15 years before the absorber cladding, a thin tube, would
show excessive thinning as a result of sliding wear.
These components were
inspected at Point Beach Nuclear Plant, Unit 2, in 1983 after 13 years of
operation.
As a result of this inspection Point Beach reported on August 18,
1983 that sliding wear was minor, but one control rod had a 2-in. crack near
the tip of the rod and severe fretting wear had occurred on several tubes.
Subsequent inspections at the Kewaunee and Haddam Neck nuclear power plants, which have been in operation for more than 12 years, confirmed the fretting
wear.
In addition, Haddam Neck reported tube cracking in 32 of 47 RCCAs.
In the event of a breach of the tubing resulting from wall thinning, perfora- tion, or cracking, the immediate effect is the introduction of activation
products from the neutron absorber material into the reactor coolant.
Although
there are large margins, another concern is the potential reduction in shutdown
margin and negative reactivity worth.
814809
.
-
IN 87-19 April 9, 1987 Discussion:
Each RCCA contains 16 rods.
The rods at Point Beach, Kewaunee, and Haddam Neck
were constructed with an outer tube of 0.019-in.-thick 304 stainless steel that
retains the absorber material (80% silver, 15% indium, 5% cadmium).
Some newer
plants use hafnium as the absorber material, while others use boron carbide
surrounded by a 0.038-in.-thick tube.
The control RCCAs are inserted or
withdrawn to compensate for various reactivity changes during operation of
the reactor and can trip to provide shutdown capability. The shutdown RCCAs
are fully withdrawn from the core when the reactor is critical.
At Kewaunee, marks of fretting wear about 1 inch in length, were found adjacent
to the guide blocks that position the rods when the RCCAs are in their withdrawn
position. The 1-in.-thick stainless steel blocks are spaced on 12-in. centers
and each rod in the cluster passes through all eight of the blocks.
At Point
Beach the tubing wore in two modes:
fretting and sliding of the rods over the
guide blocks during rod motion.
Five RCCAs at Haddam Neck had wall thinning
resulting from fretting and four of these were actually wearing into the
absorber material.
All of the others had fretting wear, but to a lesser
extent.
The fretting resulted from flow-induced vibratory contact between the rods and
the guide blocks during long periods of steady-state power operation. Vibration
is hydraulically induced by flow of the reactor coolant; therefore it is a
continuous process when the reactor coolant pumps are in operation.
According
to Westinghouse Electric Corp. fretting wear encompassed one-third of the
circumference of the rod and the depth varied with the amount of time the
RCCAs were in the withdrawn position.
At Point Beach significant number of short hairline cracks at the lower extremity
of the tubing were observed near the end plug region of the rod.
The cracks
extended axially for 4 in. and penetrated the stainless tubing, exposing the
absorber material.
No circumferential cracks were found.
Examination of the
cracks showed that irradiation-induced swelling of the absorber was the principal
cause of tensile stress in the cladding, which resulted in cracking after
substantial irradiation.
Where excessively worn rods were found, they have been replaced. While the
issue is being studied by NRC and the industry, several licensees have been
given approval to slightly change the position of the fully withdrawn RCCA in
order to distribute the wear among different locations on the tubing.
Westing- house Electric Corp. reported that an increase in the amount of the silver
isotope, Ag-110m in the reactor water is a reliable indication of exposure of
absorber material due to cracking or fretting wear.
-
IN 87-XX
April, 1987 No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact:
Paul Cortland, IE
(301) 492-4175 Attachment:
List of Recently Issued IE Information Notices
- See Previous Concurrences
D:DEPER~4:DD:DEPER:IE
ELJordan DWSASchwartz
04/ G/87K 03/10/87
- DEPER:IE
- DEPER:IE
RLBaer
JERosenthal
03/04/87
03/05/87
- DEPER:IE
PCortland:bt
02/18/87
- DEPER:IE
AWDromerick
03/02/87
- PSB:IE
DGable
03/02/87
- NRR
RLobel
02/26/87
Attachment 1
April 9, 1987
LIST OF RECENTLY ISSUED
IE INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issue
Issued to
87-18
87-17
87-16
87-15
Unauthorized Service on
Teletherapy Units by
Nonlicensed Maintenance
Personnel
Response Time of Scram
Instrument Volume Level
Detectors
Degradation of Static IIOU
Ring Pressure Switches
Complaince with the Posting
Requirements of Subsection
223b of the Atomic Energy
Act of 1954, as Amended
Actuation of Fire Sup- pression System Causing
Inoperability of Safety-
Related Ventilation Equipment
4/8/87
4/7/87
4/2/87
3/25/87
3/23/87
All NRC licensees
authorized to use
radioactive material
in teletherapy units
All GE BWR facilities
holding an OP or CP
All LWR facilities
All power reactor
facilities holding
a CP and all firms
supplying components
or services to such
facilities
All power reactor
facilities holding
87-14
86-106 Sup. 2
Feedwater Line Break
3/18/87
All power reactor
facilities holding
87-13
Potential for High Radiation
Fields Following Loss of
Water from Fuel Pool
2/24/87
All power reactor
facilities holding
Fort St. Vrain.86-106 Sup. 1
Feedwater Line Break
2/13/87
All power reactor
facilities holding
87-12
87-11 Potential Problems With
2/13/87 Metal Clad Circuit Breakers, General Electric Type AKF-2-25
All power reactor
facilities holding
All power reactor
facilities holding
Enclosure of Vital Equipment 2/13/87
Within Designated Vital
Areas
OL = Operating License
CP = Construction Permit
IN 87-XX
March, 1987 inserted or withdrawn to compensate for various reactivity changes during
operation of the reactor and can trip to provide shutdown capability. The
shutdown RCCAs are fully withdrawn from the core when the reactor is critical.
At Kewaunee, marks of fretting wear were found adjacent to the guide blocks
that position the rods when the RCCAs are in their withdrawn position. The 1- in.-thick stainless steel blocks are spaced on 12-in. centers and each rod in
the cluster passes through all eight of the blocks. At Point Beach the tubing
wore in two modes:
sliding of the rods over the guide blocks during rod motion
and fretting. Five RCCAs at Haddam Neck had wall thinning resulting from fret- ting and four of these were actually wearing into the absorber material.
All
of the others had wear, but to a lesser extent.
The tubing was worn by fretting resulting from flow-induced vibratory contact
between the rods and the guide blocks during long periods of steady-state power
operation. Vibration is hydraulically induced by flow of the reactor coolant;
therefore it is a continuous process when the reactor coolant pumps are in
operation. In general, fretting wear was 1/2-in. long and encompassed
one-third of the circumference of the rod. The depth varied with the amount of
time the RCCAs were in the withdrawn position. The worst measured depth of
tubing penetration from fretting wear was 65 percent of tubing thickness.
A significant amount of short hairline cracks at the lower extremity of the
tubing was observed near the end plug region of the rod.
The cracks extended
axially for 4 in. and penetrated the stainless tubing. No circumferential
cracks were found. Examination of the cracks showed that irradiation-induced
swelling of the absorber was the principal cause of tensile stress in the
cladding, which resulted in cracking after substantial irradiation.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact:
Paul Cortland, IE
(301) 492-4175 Attachment: List of Recently Issued IE Information Notices
- See Previous Concurrences
a
D:DEPER:IE
D~qUi
ELJordan
ZS4sz
03/
/87
03/0/87
- DEPER:IE
- DEPER:IE
- PSB:IE
- NRR
DEPER:I
DEPER:IE
PCortland:bt
AWDromerick
DGable
RLobel
RLBaer [imb
JERosenthiA
02/18/87
03/02/87
03/02/87
02/26/87
031/ /8
03/,4/87
IN 87-XX
March, 1987 inserted or withdrawn to compensate for various reactivity changes during
operation of the reactor and can trip to provide shutdown capability. The
shutdown RCCAs are fully withdrawn from the core when the reactor is critical.
At Kewaunee, marks of fretting wear were found adjacent to the guide blocks
that position the rods when the RCCAs are in their withdrawn position. The 1- in.-thick stainless steel blocks are spaced on 12-in. centers and each rod in
the cluster passes through all eight of the blocks.
At Point Beach the tubing
wore in two modes:
sliding of the rods over the guide blocks during rod motion
and fretting. Five RCCAs at Haddam Neck had wall thinning resulting from fret- ting and four of these were actually wearing into the absorber material. All
of the others had wear, but to a lesser extent.
The tubing was worn by fretting resulting from flow-induced vibratory contact
between the rods and the guide blocks during long periods of steady-state power
operation. Vibration is hydraulically induced by flow of the reactor coolant;
therefore it is a continuous process when the reactor coolant pumps are in
operation. In general, fretting wear was 1/2-in. long and included one-third
of the circumference of the rod. The depth varied with the amount of time the
RCCAs were in the withdrawn position. The worst measured depth of tubing
penetration from fretting wear was 65 percent of tubing thickness.
A significant amount of short hairline cracks at the lower extremity of the
tubing was observed near the end plug region of the rod. The cracks extended
axially for 4 in. and penetrated the stainless tubing.
No circumferential
cracks were found. Examination of the cracks showed that irradiation-induced
swelling of the absorber was the principal cause of tensile stress in the
cladding, which resulted in cracking after substantial irradiation.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact:
Paul Cortland, IE
(301) 492-4175 Attachment: List of Recently Issued IE Information Notices
- See Previous Concurrences
D :DEER:fI
K~e~t1D:DEPER:IE
AIPIR
ELJordan
02/
/87
- DEPER:IE
R
- IE
- PSB:IE
DEPER:IE DEPER:IE
DD:DEPER:IE
PCortland:bt 'AWDJomerick
DGable
RLBaer
JERosenthal
SASchwartz
02/18/87
03/i /87
03/02/87 03/ /87 03/ /87
03/ /87
IN 87-XX
February, 1987 inserted or withdrawn to compensate for various reactivity changes during
operation of the reactor and can trip to provide shutdown capability. The
shutdown RCCAs are fully withdrawn from the core when the reactor is critical.
At Kewaunee, marks of fretting wear were found adjacent to the guide blocks
that position the rods when the RCCAs are in their withdrawn position. The 1 in. thick stainless steel blocks are spaced on 12 in. centers and each rod in
the cluster passes through all 8 of the blocks.
At Point Beach the tubing wore
in two modes: sliding of the rods over the guide blocks during rod motion and
fretting. Five RCCAs at Haddam Neck had wall thinning resulting from fretting
and four of these were actually wearing into the absorber material.
All of the
others had wear, but to a lesser extent.
The tubing was worn by fretting resulting from flow-induced vibratory contact
between the rods and the guide blocks during long periods of steady-state power
operation.
Vibration is hydraulically induced by flow of the reactor coolant;
therefore it is a continuous process when the reactor coolant pumps are in
operation. In general, fretting wear was 1/2-in. long and included one-third
of the circumference of the rod. The depth varied with the amount of time the
RCCAs were in the withdrawn position. The worst measured depth of tubing
penetration from fretting wear was 65 percent of tubing thickness.
A significant amount of short hairline cracks at the lower extremity of the
tubing was observed near the end plug region of the rod. The cracks extended
axially for 4 in. and penetrated the stainless tubing.
No circumferential
cracks were found.
Examination of the cracks showed that irradiation-induced
swelling of the absorber was the principal cause of tensile stress in the
cladding, which resulted in cracking after substantial irradiation.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the Regional
Administrator of the appropriate regional office or this office.
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact:
Paul Cortland, IE
(301) 492-4175 Attachment:
List of Recently Issued IE Information Notices
D:DEPER:IE
ELJordan
02/
/87 DEPE
f
i
DEPER:IE
PSB:I p, DEPER:IE DEPER:IE
DD:DEPER:IE
PCo la
t
AWDromerick
DGabl
RLBaer
JERosenthal
SASchwartz
02/ /87
02/ /87
792/, /87 02/ /87 02/ /87
02/ /87